Getting better all the time

Design Engineering takes a look at the latest fuel cell cars and discovers that new fuel cells can even run on petrol!

Cars powered by fuel cells, typically running from hydrogen fuel, offer the promise to make the dream of a low emissions automobile a fact. Fuel cells have several advantages over batteries, which currently have range and durability limits.

Despite their advantages, some technical hurdles still remain to be overcome before we are all driving one of these environmentally friendly beasts. The packaging and weight of the fuel cell in the car may be as difficult to overcome as will be the building of an infrastructure that can support such vehicles.

That has not stopped a group of the world’s leading automobile manufacturers from developing automobiles powered by these fuel cells. Earlier in the year, DaimlerChrysler introduced a fuel cell car that demonstrated a 40% increase in fuel cell power over its earlier fuel cell models while also offering three times the range of a battery powered car.

Dubbed the Necar 4 (for New Electric Car), The DaimlerChrysler design uses fuel cells to generate electricity and water. Based on a Mercedes Benz A class compact car, the vehicle is capable of reaching speeds of up to 90mph (compared to a top speed to 68mph in its predecessor) and can travel nearly 280 miles (450km) before refuelling.

In addition, engineers have been able to mount the entire fuel cell system in the floor of the vehicle for the first time, because, the energy density of the fuel cell system has increased by a factor of four since Necar 1 was introduced four years ago. The car now has room for up to five passengers as well as cargo space.

In the Necar 4, liquid hydrogen is stored in a cryogenic cylinder resembling a large thermos at the rear of the vehicle. The fuel is then processed by a Proton Exchange Membrane (PEM) fuel cell. Each PEM fuel cell is composed of many cells, each having two electrodes (anode and cathode) with a polymer electrolyte compressed between the two electrodes. The electrodes are electronically conductive and in contact with a thin catalyst layer (typically platinum) embedded in the polymer electrolyte surface to facilitate the conversion reactions.

Inside the PEM FC, the platinum coated membrane separates hydrogen into protons and electrons and combines them with oxygen in the air to form water. This surplus and deficit of electrons and protons produce electricity, which, in turn, powers the vehicle.

Fuel cells have a theoretic maximum efficiency of 83%, but the practical efficiency ranges from 50 to 60%, a little more than twice as efficient as an internal combustion engine.

But of course, DaimlerChrysler is not the only horse in the race. This year, Ford also debuted a hydrogen fuel cell sedan called the P2000. This fuel cell car was designed to achieve the performance of a Ford Taurus, which sports an acceleration from 0 to 60mph in 12sec.

Both Ford and DaimlerChrysler are researching fuel cells in partnership with Ballard Power systems. In the Ford design, the electric power also comes from Ballard’s PEM cells. These are considered to be the most promising for automotive applications out of the three types of cells that are currently available: these being a phosphoric acid fuel cell and a solid oxide fuel cell.

At General Motors, engineers are investigating a series hybrid electric vehicle, the EV1, that draws its primary energy from an onboard fuel cell and supplementary energy from the batteries.

GM has mounted a fuel cell advanced propulsion system in its EV1 that has been stretched 19in to create additional space for a total of four passengers. The fuel cell stack consists of many individual cells that have been sandwiched together. The cells in a stack are electrically connected in a series to provide an appropriate voltage. The cells are fed a hydrogen-rich mixture, called `reformate’, and filtered compressed air. The compressed air provides oxygen, which reacts with hydrogen to form water and creates a voltage across each cell.

In the GM design, the multi-stage fuel processing system converts methanol into a hydrogen-rich mixture which is used as the source of hydrogen for the fuel cells. An expander compressor is designed to capture energy that would be otherwise lost in the exhaust gases from the fuel cells. All remaining hydrocarbons are combusted, resulting in a hot stream of water-rich gas which is used to heat the reformer. This gas is then run through an expander that cools the gas by removing energy as mechanical force, much like a steam powered turbine-generator. The mechanical force is used in addition to an electric motor to drive a compressor that supplies the compressed air to the fuel cells.

The fuel cell electric EV1 is capable of more than 300 miles and can be charged safely in all types of weather conditions using a system known as `inductive charging’.

Charging requires less than 2hr using a 220V charger. The EV1 is powered by a 137hp, 3-phase, AC induction motor and uses a single-speed, dual reduction gear-set with a ratio of 10.946:1.

Like GM, Toyota are also working on fuel cells that use methanol as the basic fuel to provide hydrogen to the fuel cell. Toyota’s Fuel Cell Electric Vehicle is an experimental version of a electrically-powered RAV4 vehicle that does not need recharging. The Toyota fuel cell is comprised of four main components: a methanol storage tank, a conversion device, a fuel cell stack and a permanent-magnetic electric motor. Toyota claims that its fuel cell has an energy conversion rate of over 60%.

{{Ford Motor


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